The Japanese government said Tuesday it will offer free rubella vaccinations for three years to men who were unvaccinated in their childhood amid an outbreak of the disease that threatens to dampen demand for travel to Japan.

Rubella can have serious health impacts on unborn babies and vaccinations and antibody tests will be offered free, in principle, through March 2022 for men aged between 39 and 56 who were not vaccinated under regular public programs.

The number of rubella patients in Japan has reached 2,454 this year, topping the figure for 2012 when the previous outbreak began, and the spread is believed to be mainly caused by unvaccinated men in the targeted age group.

Tests and vaccinations will be administered at medical institutions in residential areas from early next year.

If unborn babies are infected with rubella through their mothers in the early stages of pregnancy, they can suffer birth defects such as hearing impairments, cataracts and heart disorders.

The government will call for cooperation from businesses and clinics so that people can take antibody tests during regular health examinations in the workplace, or get vaccinations at night or on weekends at medical institutions.

In late October, the U.S. Centers for Disease Control and Prevention raised its alert level for the rubella outbreak in Japan to Level 2, the second highest of 3 levels, warning that pregnant women should not travel to the country unless protected against the disease through vaccination or previous infection.

To ward off a potential vaccine shortage, people are first asked to take antibody tests. Both antibody tests and vaccinations will be free for men born between April 2, 1962 and April 1, 1979 in the three-year period.

Although 92 percent of Japanese are immune to rubella, the percentage falls to about 80 percent for men in the targeted age group. The government aims to raise the proportion to 85 percent or more by the Tokyo Olympics and Paralympics in 2020 and to over 90 percent by the end of March 2022.

According to the World Health Organization, 85 percent of people in all generations need to be immunized against the disease to attain herd immunity that can prevent a disease from spreading.